1. Chronic Restrictive Pulmonary Disease
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Chronic restrictive pulmonary disease (CRPD) encompasses a range of heterogeneous disorders that are characterized by a low lung volume and reduced thoracic or lung compliance or both.
These disorders result from diverse pathological processes involving the chest wall, respiratory muscles, and nerves serving the thorax, as well as the pleura and lung parenchyma.
They are termed restrictive because they restrict the bellows mechanisms of the lung, which is in contrast to obstructive lung disease that prevents airflow by obstructing the airways.
People with restrictive lung disease cannot fully fill their lungs with air. Their lungs are restricted from fully expanding.
Restrictive lung disease most often results from a condition causing stiffness in the lungs themselves. In other cases, stiffness of the chest wall, weak muscles, or damaged nerves may cause the restriction in lung expansion.

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Anatomy

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The diverse pathophysiological mechanisms that cause CRPD can be categorized with the following categories:
Extrapulmonary Disorders
Neuromuscular (ex. muscular dystrophy)
Trauma and Mechanical (ex. obesity, fibrosis)
Intrinsic Pulmonary Disorders
Interstitial Inflammation
Pulmonary Vascular Disease
Inhaled Particles (ex. Asbestos)
In the parenchymal conditions, alveolar–capillary units are destroyed or replaced by fibrous tissue.
In conditions involving the pleura, chest wall, or neuromuscular system, the lung is intrinsically normal but respiratory efforts are unable to expand the lung parenchyma, leading secondarily to alveolar collapse, inflammation, and eventually fibrosis.
Regardless of specific etiology, these are the common end results:
Loss of alveolar–capillary surface area and volume
Impaired oxygen transfer across the pulmonary blood–gas barrier

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Development of clinical symptoms may be acute (days), subacute (weeks), or chronic (months to years). The most common symptom is shortness of breath upon exertion, and a dry cough and pleuritic chest pain may also be present.
Patients may hyperventilate in mild to moderate stages and have rapid shallow breaths in advanced stages.
Lung function testing shows reduced lung volumes, with airflow rates reduced in proportion to the reduction in lung volume.
One of the most important physiological consequences of CRPD is the effect it has on the work of breathing.
Compliance of the lung or thorax is reduced, requiring a more negative airway pressure to inflate the lung. Hence, respiratory muscles work harder (i.e., increased work of breathing).

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Tidal volume (the lung volume representing the normal volume of air displaced between normal inhalation and exhalation when extra effort is not applied) is reduced while dead space is elevated, so ventilation becomes less efficient, further increasing the work of breathing needed to maintain a given oxygen uptake by the lungs.
A larger fraction of total body metabolic energy must be diverted to respiratory muscles to sustain a given level of ventilation, leaving a smaller fraction available for working limb muscles during exercise. This leads to greater lactic acid production from exercising limb muscles, further stimulating ventilation and increasing the work of breathing.
Restriction of pulmonary vascular bed increases pulmonary vascular resistance, leading to secondary pulmonary hypertension, right ventricular strain, and a lower stroke volume during exercise.

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Medical treatment of CRPD must be tailored to the specific pathology.
The general approach is to first identify and treat the underlying cause:
Orthopedically correct spinal deformity in kyphoscoliosis.
Treat bacterial, viral, or fungal infections.
Suppress inflammatory and immunologic activity in the intrinsic lung conditions (usually with inhaled or systemic corticosteroids, immunosuppressants, cytotoxic or antifibrotic agents).
Secondarily, management is aimed at minimizing pulmonary complications related to the abnormal lung physiology:
Institute chest physiotherapy to clear secretions (mainly neuromuscular diseases).
Prevent infections, for example, prophylactic antibiotics, regular vaccination, clearing secretions.
Support oxygenation, for example, supplemental oxygen therapy.
Third, it is important to preserve normal physical and physiological functions as much as possible, to both maintain physical functioning and avert cardio-metabolic conditions secondary to being sedentary:
Optimize cardiopulmonary and muscular fitness with a rehabilitation program.
Then maintain physical functioning with a regular exercise regimen.
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In individuals with CRPD, management involves treating the underlying cause of restrictive pathology and using pulmonary rehabilitation to preserve respiratory function.
Ultimately, some people develop respiratory failure or severe abnormalities in gas exchange requiring noninvasive positive pressure ventilation. They may end up being evaluated for lung transplantation
Drugs commonly used in management of interstitial lung disease include the following:
Anti-inflammatory and immunosuppressant drugs (ex.—prednisone)
Prophylactic antibiotics
Supplemental oxygen

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Effects on the Exercise Response
Reduced exercise tolerance and dyspnea upon exertion are common.
The typical breathing pattern at rest consists of rapid shallow breaths, and with exercise the minute ventilation (the volume of gas inhaled (inhaled minute volume) or exhaled (exhaled minute volume) from a person's lungs per minute. ) increases atypically because of increased forces required to expand the chest
Ventilatory factors contributing to dyspnea and exercise limitation include:
Inefficient ventilation with a high dead space
Mechanoreceptor stimulation
Heightened central respiratory drive

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Effects on the Exercise Response
In early restrictive disease, the alveolar–arterial oxygen tension gradient is typically elevated while arterial oxyhemoglobin saturation remains above 90%.
In moderate to severe restrictive disease, arterial oxygen saturation breathing room air may be above 90% at rest but decline to below 90% upon exercise.
Finally, in end-stage lung disease, the resting arterial oxygen saturation is reduced below 90% and arterial carbon dioxide tension begins to rise above normal, indicating respiratory failure

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Effects of Exercise Training
Exercise training has multiple benefits in restrictive lung disease:
Improving submaximal exercise endurance
Improving maximal oxygen uptake, depending on initial fitness level
Improving ventilatory endurance, efficiency, and ventilation–perfusion matching
Improving cardiovascular conditioning
Increasing peak exercise lung diffusion capacity as peak cardiac output increases
Improving oxygen extraction, skeletal muscle endurance, and efficiency
Reducing oxygen and blood flow requirement of respiratory muscles, increasing the amount available to working limb muscles
Reducing lactic acidosis to reduce ventilatory stimulation from exercise
Desensitizing the perception of dyspnea and the fear of exertion

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Recommendations for Exercise Testing
Exercise testing is an important tool for assessing the impact of CRPD on physical functioning.
Goals of exercise testing include :
Defining disability due to pulmonary dysfunction
Detecting coexistent factors that aggravate disability
Monitoring progression of impairment and response to therapy
The most common clinical exercise assessment is a 6-min walk test with concurrent transcutaneous measurement of pulse rate and oxygen saturation. If desaturation occurs during the test, the test can be repeated while administering supplemental oxygen.
Following a resistance-free warm-up period, work rate should be increased in small increments. Electrocardiogram, systemic blood pressure, and transcutaneous oxygen saturation should be monitored. Minute ventilation, respiratory rate, tidal volume, and basic ventilatory gas exchange analysis (oxygen uptake, CO2 output) are commonly measured during exercise. Supplemental oxygen may be added as needed.

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Recommendations for Exercise Testing
Clinical indications for terminating exercise :
chest pain,
faintness,
dysrhythmias,
drop in blood pressure below resting level or
hypertensive response,
persistent inability to maintain oxygen saturation above 90%,
or volitional termination of exercise due to fatigue or shortness of breath.
Chronic restrictive pulmonary disease–related contraindications to exercise testing have to do with severe symptoms and secondary conditions :
Severe pulmonary arterial hypertension
Unstable heart failure, ischemic or valvular cardiac diseases
Life-threatening dysrhythmias
Pre-syncope, syncope

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Recommendations for Exercise Programming
The Basic Exercise Prescription recommendations are generally advised for persons with CRPD. Emphasis on maintaining physical functioning and independent living is appropriate for most individuals with CRPD.
An initial period of intense training (20-30 min/day, 5 days a week for 6-8 weeks) is helpful in establishing a baseline level of fitness, and sustained training thereafter can be continued three times a week.
For subjects with poor exercise endurance, a training session may be divided into several shorter segments with rest periods in between. Regular follow-up assessment of exercise and pulmonary function will quantify any improvement or decline in function.
Special Considerations
Worsening hypoxia during exertion may induce chest pain, arrhythmias, or both. People should take medications as usual to obtain the best exercise performance. Supplemental O2 flow rate should be adjusted to maintain O2 saturation >90%. Anxiety, depression, and fear avoidance are common barriers.
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